Severe vitamin D deficiency diagnosed after introduction of antiretroviral therapy including efavirenz in a patient living at latitude 59°N

HIV-infected individuals have an increased risk of osteopenia, osteoporosis and osteomalacia [1–3]. The aetiology is multifactorial [4,5]. We report the case of a previously healthy Ethiopian man, who had migrated to Sweden in the early 1990s, was HIV-negative in 1996, but was diagnosed with asymptomatic HIV infection in April 2002. His CD4 cell count was 180 × 106 cells/ml. His plasma viral load was 205 000 HIV-1-RNA copies/ml. His body mass index was 20.5. He was a strict vegetarian. Clinical signs of rickets or osteomalacia were absent. In June 2002, treatment with zidovudine, lamivudine and efavirenz was initiated. Liver enzymes were within the normal range, and were followed routinely at clinical visits. During autumn, serum alkaline phosphatase (ALP) increased to 11.7 μU/l (reference range 0.8–4.6), whereas serum transaminase levels remained normal. Fractionated ALP analysis revealed a dominance of skeletal isoenzymes. Bone scintigraphy and prostate-specific antigen was unremarkable. Parathyroid hormone (PTH) was elevated to 100 ng/l (reference 10–65) in June 2003 and 205 ng/l in July 2003, in the presence of a normal calcium level (2.32 mmol/l, reference 2.20–2.60) indicating secondary hyperparathyroidism. The preferred laboratory analysis to evaluate nutritional vitamin D status is 25(OH) vitamin D in serum. In December 2003, this was below the detection limit (< 18 nmol/l, reference 25–125). The cause of the elevated PTH and ALP was considered to be vitamin D deficiency. Dual X-ray absorptiometry (Hologic, Bedford, Massachusetts, USA) in February 2004 revealed a bone mineral density with a T-score of −3.13 in the lumbar spine and −3.84 in the left hip, 70% and 64%, respectively, of the mean age-matched values. In December 2004, after approximately one year of supplementation with vitamin D2 (175 μg/week), vitamin D3 (20 μg/day) and calcium (1000 μg/day) serum ALP and PTH levels were within normal limits. A dual energy X-ray absortiometry measurement after 9 months of supplementation showed an improvement of bone mineral density by 4% in the lumbar spine and by 11% in the femoral neck. Bone tissue is constantly turned over. Vitamin D is necessary for maintaining calcium homeostasis and for the mineralization of the bone matrix. Adult vitamin D deficiency is associated with osteomalacia, muscle weakness and lower back pain [6,7]. The main vitamin D source is 7-dehydrocholesterol, which is transformed into vitamin D3 in the epidermis when unprotected skin is exposed to sunlight. Vitamin D-enriched dairy products and fat fish are other sources of vitamin D (Fig. 1).Fig. 1: Schematic illustration of vitamin D formation, activation and possible sites where efavirenz may interfere. After formation in the epidermis, vitamin D is first converted to 25(OH) vitamin D in the liver. Parathyroid hormone regulates the 1-α-hydroxylation of 25(OH) vitamin D to biologically active 1,25(OH)2 vitamin D in the renal tubuli. 1,25(OH)2 vitamin D is inactivated by 24-hydroxylation. Efavirenz might affect both the hydroxylation and inactivation of vitamin D through the induction of CYP3A4 and CYP24, respectively. PXR, Pregnane X receptor; UV, ultraviolet.In Stockholm, at latitude 59° north, virtually no vitamin D is produced in the skin during the dark winter months. At this latitude, highly pigmented skin is a risk factor for vitamin D deficiency [8,9]. Several enzymes have been implied in the 25-hydroxylation of vitamin D, including the mitochondrial CYP27A and the microsomal CYP2R1 [10]. CYP3A4 was recently shown to be a vitamin D 25-hydroxylase [11]. Efavirenz is an inducer of CYP3A4. The inactivation of active vitamin D is catalysed by CYP24, which is inducible through pregnane X receptor activation, the pathway through which efavirenz is presumed to cause its induction of CYP3A4 [12,13]. Efavirenz could thus affect both the availability of substrate for 1-α-hydroxylation, and the kinetics of 1,25(OH)2 vitamin D inactivation. Notably, there are several published reports in which chronic treatment with CYP450 enzyme-inducing antiepileptic agents was associated with decreased levels of 25(OH) vitamin D and elevated serum ALP [14–16]. Controlled studies concerning the effect of efavirenz on vitamin D homeostasis are not available. However, one observational study detected significantly lower 1,25(OH)2 vitamin D levels in patients on protease inhibitors or non-nucleoside reverse transcriptase inhibitors, compared with treatment-naive HIV-infected controls [17]. Another publication described the in-vitro inhibition of hepatocyte 25-hydroxylation of vitamin D by nelfinavir, indinavir and ritonavir [18], implying that these protease inhibitors might affect vitamin D homeostasis. In our patient ALP elevation developed after the initiation of antiretroviral therapy. PTH rose dramatically despite sun exposure during the summer season. We suggest that CYP450 enzyme induction by efavirenz might have affected vitamin D metabolism, resulting in an aggravation of a pre-existing vitamin D insufficiency caused by nutritional habits and less vitamin D synthesis in the skin. Further studies on the effect of chronic treatment with CYP enzyme inhibitors and inducers, such as efavirenz and ritonavir, on vitamin D and other endocrine functions are mandated. Risk groups should be screened for subclinical vitamin D deficiency before starting therapy.